Threaded tubular structure



July 19, 1949.

Filed Dec. 4, 1945 A. w. GALBRAITH 2,476,656

THREADED TUBULAR STRUCTURE 2 Sheets-Sheet 1 IN V EN TOR.

ALEXANDER WGALBRAITH.

ATTORNEYIS.

July 19, 1949. A. w. GALBRAITH 2,476,656

THREADED TUBULAR STRUCTURE Filed Dec. 4. 1946 2 Sheets-Sheet 2 ATTO R NCV5.

Patented July 19, 1949 UNITED STATES PATENT OFFICE THREADED TUBULARSTRUCTURE Alexander William Galbraith, Houston, Tex. ApplicationDecember 4, 1945, Serial No. 632,688 2 Claims. (Cl. 285-146) Thisinvention pertains to metal tubes of steel, copper, brass, aluminum,duraluminum, or other metal capable of being formed under pressure, theopposite ends of which tube are provided respectively, with equally andoppositely tapered, rolled-in threads of substantially uniform wallthickness corresponding to that of the body 01' the tube, said threadedends being of enhanced strength due to cold working, and providing ameans for detachably uniting successive tubes in substantiallyfluid-tight joints without the necessity for intermediate threadedcoupling members. The invention also pertains to novel methods andapparatus for providing said metal tubes with threaded terminations asaforesaid.

Difliculties have been encountered in the past in devising suitableconstructions for detachably joining metal pipes or other metal tubes influidtight connections. The usual procedure is to provide the pipe ortube terminations with cut threads, and to join successive sections bymeans of internally threaded pipe couplings. The cutting of suchthreads, however, by reducing the wall thickness of the tubular stock inthe threaded portion, thereby weakens the construction. In addition, thenecessity for employing in conjunction therewith the threaded couplingsis expensive, first, by reason of the necessity for and expense of thecoupling itself; and, second, by reason of the two threading operationsrequired, viz., the external threading of the pipe ends and the internalthreading of the couplings. The use of such cut threads obviously limitsthe permissible wall thickness of the tubular stock which may beemployed in any particular installation, and, conversely, necessitatesthe employment in the body or non-threaded portion of the stock, of agreater wall thickness than would otherwise be required.

In accordance with my invention, I propose to eliminate the diflicultiesaforesaid, while at the same time actually increasing the strength atthe joint by providing the opposite ends of the metal tubesrespectively, with equally and oppositely tapered, rolled-in threads,such that the wall thickness in the threaded portion is in no wisereduced, but is maintained the same as that of the body of the tubeproper, and wherein the cold working which results from the threadingand tapering of the end portions of each tube, actually enhances thestrength of the metal in the threaded portions, whereby with myinvention, the metal at the joint is actually stronger than in the bodyof the tube, in marked contrast to prior constructions employing cutthreads.

By means of these improvements, I am able to employ, for any particularinstallation, metal tubing of considerably reduced wall thickness ascompared to prior constructions employing out threads, this by reason ofthe cumulative effect of the two factors above stated, namely, theavoidance of any reduction in wall thickness in the threaded portion,and the enhancement in strength at the joint due to cold working of themetal thereat.

In accordance with the preferred embodiment of the invention, t e metalin the threaded portions of each tube s slightly expanded in diameter,prior to threading and tapering, over the diameter of the main body ofthe tube, and to such an extent that the threaded junction formed bydetachably uniting two of the threaded and tapered finished articleswill have about the same internal diameter as the main body of thetube, 1. e., there will be noreduction or constriction in diameter atthe threaded joint, and hence no obstacle to the passage of fluids orother materials therethrough.

In my preferred process for making the article above described, asection of steel, brass, copper, or other cold deformable metal tubing,is placed upon an arcuate support and the end thereof advanced axiallyover the threaded end of a threading mandrel of slightly greaterdiameter, thereby slightly to expand or flare the end of the tube overthe axial length thereof which it is desired to thread. This forcing ofthe end oi. the tube over the threading mandrel may be accomplished bymeans of an hydraulic ram engaging the opposite end, the threadingmandrel being meantime stationarily positioned. When the end of the tubehas thus been advanced a sufiicient distance over the mandrel to flarethe end of the tube over the desired axial extent, the hydraulic ram iswithdrawn and the threading mandrel, carrying with it the tube, isadvanced in threading relation, 1. e. by concurrent axial advance androtation, through the aperture of an external, stationary,roll-threading die, whereby, by c0-acti0n between this externalroll-threading die and the threading mandrel advancing the tubetherethrough, a thread is rolled on the expanded or flared end of thetube. When the threading mandrel, carrying with it the tube, has thusadvanced completely through the stationary roll-threading die, the tubeis gripped in a clamp to hold it stationary, and the direction ofrotation of the threading mandrel reversed and the mandrel concurrentlyaxially withdrawn from threading engagement with the threaded end of thetube, whereupon the threading opcration for this end of the tube iscomplete. The opposite end of the tube is thereupon expanded andthreaded by an identical procedure. The tube. with both ends thusexpanded and threaded, is now placed between a tapered die and a taperedmandrel, and the die and manare] advanced toward each other, as forexample by means of an hydraulic ram, thereby to force the taperedmandrel into one threaded end of the tube, while the opposite threadedend thereof is concurrently forced into the tapered cavity of the die.In consequence of this operation, the threaded end of the tube whichenters the die has imparted thereto a taper which extends inwardlytoward the end thereof, while the opposite threaded end of the tube,which is penetrated by the tapered mandrel, has imparted thereto anequal and opposite taper which extends outwardly toward the end thereof.By reason of the tapered configurations thus imparted to the threadedends, the inwardly tapering threaded end of one tube is adapted to bethreaded into the outwardly tapering end of a similar tube, to form theaforesaid fluid-tight joint.

Having thus generally described the preferred embodiment of my inventionas to the novel product and the novel method for producing the same,reference will now be made. for a more detailed description, to theannexed drawings wherein:

Figure 1 is a plan view of a metal tube, the opposite ends of which areprovided respectively with equally and oppositely tapered, rolled-inthreads, in accordance with the preferred embodiment of my invention.

Figure 2 is a view in axial section through the Joint of two metal tubesin accordance with my invention, as detachably united.

Figures 3 to '7 inc. are plan views, partially in section, illustratingthe successive steps of my novel process for rolling the threads intothe metal tubes. Figure 8 is a view in elevation of the stationaryexternal threading die illustrated in side view in Figures 3 to 7 inc.,employed in the threading operation as described more in detailhereinafter.

Figures 9 and 10 are plan views of the successive steps employed in myprocess for impartin equal and opposite tapers to the threaded ends ofthe metal tubes.

Referring to Figure 1, there is shown a metal tube I, the opposite ends2, 8 of which are provided respectively with expanded and oppositelytapered, complementary rolled-in threaded terminations. terminus 8 beingprovided with a reduced taper toward the end, and the opposite terminus1 being provided with a corresponding increased taper toward the end,whereby successive tubular members, like those of Figure 1, may bedetachably united in a substantially fluid-tight joint, in the mannerillustrated in Figure 2. In Figure 1, the degree of taper of thethreaded ends is exaggerated, for purposes of illustration, the actualtaper being more in line with that illustrated in Figure 2.

Referring to Figure 2, there is illustrated at the left, one threadedend of a tubular member I, in accordance with my invention,corresponding to the end I in Figure 1, via, the end having a reducedtaper toward the end; while, at the right in Figure 2, there isillustrated the opposite threaded end of another tubular member ofsimilar construction and corresponding to the end 2 of Figure 1, havingan increased taper toward the end. As shown in Figure 2, the end of 4the member 4 having reduced taper is adapted to thread into theoppositely tapered end of the tubular member 5, to provide the aforesaidsubstantially fluid-tight joint.

It ,will be observed from the cross-sectional showing of Figure 2, thatthe wall thickness of the tube stock in the threaded portion, as at i,is substantially constant, and the same as that in the body portion 1 ofthe tubular member proper. That is to say, in the formation of thethreads, no metal has been cut away, and also there is no substantialvariation in wall thickness of the metal in the threaded portion, ascompared to the body portion of the tube. In other words the wallthickness of the metal in the crest,

root and sides of the threads is substantially equal to the wallthickness of the metal in the non-threaded or body portion of the tube.It will be further observed that, by virtue of the complementary tapersimparted in the threaded portions of the members l, 5 thus detachablyunited, a locking action occurs at each thread, whereby the aforesaidfluid-tight joint is secured.

Referring now to Figures 3 to 8 inc. for a detailed explanation as to mypreferred method for forming the threads, referring for the moment toFigure 3, there is shown a mandrel 8 provided with a threaded head I!adapted to cooperate with a stationary external roll-threading die In,to roll the threads in the tubular stock as explained below. Thestationary roll-threading die "I, as shown more in detail in Figure 8,comprises a circular frame ll stationarily mounted on rigid supports l2,and within which one or more rollthreading dies, such as at l3, l4, l5,are rotatably supported on shafts, such as l6, carried by the frame H.As illustrated more in detail in Figure 5, each of the roll-threadingdies, such as I3, is provided on its periphery with a threaded formwhich is complementary to the threaded form 9 on the threading mandrel8. The threaded portion 9 of the threading mandrel 8 is of slightlygreater diameter than the internal diameter of the metal tube is to bethreaded.

Prior to the threading operation, the threading mandrel 8 is positionedto the left of the stationary roll-threading die I! in the relativeposition thereto shown in Figure 3, while the metal tube I8 ispositioned to the right of stationary die ill on an arcuate support is.One end 20 of tube is is thereupon forced over the threaded portion 9 ofmandrel 8 by means of a power actuated ram 2| engaging the opposite end22 of tube is, which ram may be actuated by any suitable means such ashydraulic pressure, compressed air, etc., and in such manner as to exertcontinuous pressure on the tube II in the direction indicated by thearrow 23, until the end 20 of the tube has been forced over the threadedportion 9 of the mandrel I from the initial position shown in Fig. 3 tothe final extent illustrated in Figure 4, i. e. the extent over which itis desired to thread the end 20. It will be observed that. as a resultof this operation, the end 20 of tube is has been expanded or flaredoutwardly to a slight degree as compared to the remainder or main bodyportion of tube ll. When the end 2. of tube It has thus been expanded orflared over the desired axial length, depending on the length over whichthe threading is required. the pressure exerted by the hydraulic ram 2|is released by withdrawal of the ram II to the position 24, Figure 4.

Referring to Figure 5, the threading mandrel t, carrying with it thetube II, is now rotated and concurrently advanced, as indicated by thearrows 25, actuated, for example, by means of a power-driven lathe,whereupon the outer surface of the expanded portion 2|! of tube Itengages the form-threaded rolls l3, ll, iii of the stationaryroll-threading die In, while at the same time the threaded portion 9 ofthe mandrel engages the inner surface of the expanded portion 2i] oi thetube in such manner that, by the co-action between the threaded portionof the mandrel and the form-threaded rolls on the stationary threadingdie, threads are rolled into expanded section of the tube in the mannerillustrated in Figure 5, the concurrent rotation and advancement of themandrel, from the power source, being appropriately adjusted to carryout this operation.

The aforesaid advancement of mandrel 8 is continued until the mandrel,carrying with it the tube l8, has advanced to the position shown inFigure 6, in which the threaded end 9 of the mandrel has movedcompletely to the right of the stationary threading die to. At thispoint, an upper clamping member cooperating with the tube support I9 isoperated, thereby to grip the tubular member l8 between members I9, 25,whereupon the power drive on the threading mandrel B is reversed causingthe mandrel to be withdrawn to the left and concurrently rotated, asindicated by arrows 2B, Figure '7, thereby to disengage the mandrel fromthe threaded portion 2|) of the tubular member, as shown in Figure '7,this operation continuing until the threading mandrel 8 has reassumedthe position shown in Figure 3.

Identically the same sequence of operations as above described is nowperformed on the opposite end of the tube l8, thereby to expand andthread the opposite end 22 thereof. The thus threaded tubular memberthen has the appearance shown in Figure 9.

The so-threaded tubular member is is now placed between a tapered die 21having a tapered cavity '6, and a mandrel 29 having a similarly taperedstud 30, and pressure exerted between the mandrel and the die by anysuitable means, as for example by means of an hydraulic ram, compressedair, power driven screw feed, etc. This pressure is continued until thethreaded end 20 of tube Iil has been forced sufiiciently into the cavity28 of the die, and until the stud ii of the mandrel has sumcientlypenetrated the threaded end 22 of tube It to oppositely taper theseends, as illustrated in Figure 10. In consequence of this operation, theleft end 20 of the tubular member has imparted thereto a reduced tapertoward its end, while the opposite end 22 of the tubular member hasimparted thereto a complementar increasing taper toward its end. At thispoint in the sequence of operations, the mandrel 29 is withdrawn byrelease from the hydraulic pressure and the tubular member l8 removedfrom the die, resulting in the finished structure as illustrated inFigure 1.

Although the above describes the preferred modification of my invention,and the preferred process for making the same, various othermodifications are possible. For example, the tubular member may beprovided with non-tapered threaded ends, by expanding and threading oneend as illustrated in Figures 3 to 7 inc., while threading the oppositeend without expansion, in which event "Lc non-expanded threaded end ofone tubular member will thread into the expanded and threaded end ofanother tubular member, thereby to form the joint. Another modificationwould comprise expanding both ends, one slightly more than the other,followed by threading, to provide a threaded telescoping joint. Inanother possible modification, the two ends of the tubular member may bethreaded without expanding the diameter of the end portions, followed bythe imparting of equal and opposite tapers to the ends so threaded, inthe manner illustrated in Figures 9 and 10. In this modification, theopposite tapers imparted to the two threaded ends, are the means bywhich the end of one tubular member having decreasing taper may bethreaded into the opposite end of another member having increasingtaper.

Slight changes in the method above described for making my preferredmodification of the invention are entailed in producing the modifiedstructures above mentioned. For example, the rolling of a thread into anon-expanded terminus of a tubular member is best effected by employingan external roll-threading die having a rolldisengaging construction fordisengaging the thread when finished, this being accomplished, forexample, by the use of self-closing rollers on the external die; and byfurther employing a construction of the threading mandrel adapted todisengage the threads, such for example as a collapsible mandrel, or onehaving threading rolls which canbe disengaged.

The invention is applicable to tubular members made of any metal capableof being formed and shaped under pressure, such as low carbon steel,austenitic stainless steel, copper, brass, aluminum, duraluminum, etc.Ordinarily, the expanding threading and tapering at the ends of thetubular members, in accordance with the invention, are carried out bycold working the metal; although my invention does not preclude carryingout these operations at elevated temperatures, particularly wheretubular members of considerably wall thickness are required for anyparticular installation. A marked advantage of carrying out theseoperations on the metal "in the cold is that the metal at the joint isthereby cold worked, and correspondingly strengthened as aforesaid, andfor this reason I prefer the use of cold-working operations wherefeasible and applicable. though the wall thickness of the tubularmembers is not critical, I find that excellent results are obtained byapplying the invention to metal tubes having a wall thickness of, forexample 1 5 to /8 inch, preferably about 1 to 3 1 inch, although greateror lesser wall thicknesses may be employed. For any given metal,however, the wall thickness should be sufficiently great to provide arelatively rigid tube, and one which will retain its shape at the jointswhen expanded, threaded and tapered as aforesaid, and thereby be capableof providing the fluid-tight joints where required, although there are,of course, applications where this is not necessary and to which variousmodifications of my invention are equally applicable.

It is to be understood of course, referring to Fig. 4, that the externalroll threading die I, need not necessarily be held stationary during thethreading operation, but may be advanced against the stock by means of apower actuated screw feed in the same fashion as the threading mandrel8, in which case the threading mandrel could be maintained stationar ifdesired.

I claim:

1. A cylindrical tube of substantially uniform wall thicknessthroughout, made of metal capable of being formed under pressure, saidtube being provided at each end with a complementary ex- QA'IUJIO ternaland internal, rolled-in, threaded terminus of sinuous term inlongitudinal section and oi substantially unii'orm wall thicknessthroughout. corresponding to that of the body of the tube, said threadedportions being work-hardened throughout and of enhanced strength, andthe threaded terminus at one end being adapted to threadedly engage thethreaded terminus at the opposite end or a similarly constructed tube.

2. A cylindrical tube of substantially uniform wall thicknessthroughout, made of metal capable of being formed under pressure, saidtube being provided at each end with a complementary external andinternal, rolled-in, threaded terminus of sinuous form in longitudinalsection and of substantially uniform wall thickness throughout,corresponding to that of the body 01 the tube. the threaded portions atthe opposite ends having imparted thereto equal and opposite tapers.whereby the threaded portion at one end is adapted to threadedly engage,in a substantially 'fluid tight joint, the threaded portion at theopposite end 01 an similarly constructed tube, abd the metal in saidthreaded portions being sufliciently 8 expanded in diameter comparedwith the body 0! said tube. to provide a threaded joint as aforesaid,

having a minimum diameter corresponding sub-,

stantlally to the internal diameter of the body of said tube, and themetal in said threaded portlons being work hardened throughout and oienhanced strength.

ALEXANDER WILLIAM GALBRAITH.

REFERENCES CITED The following reierenices are of record in flle oi.this patent:

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